The present invention relates to a projection screen for image reproduction devices which comprise projectors and screens, an image being projected onto the rear side of a screen with the aid of a projector. The field of application is that of multi-screen displays.
In the case of a multi-screen display of this nature, the viewer is situated in front of the screens, which are positioned next to and/or above one another, optionally at an angle, so that they form an image surface onto which an image, optionally composed of a plurality of subimages, can be projected. A subimage may cover one or more screens of the image surface and may occur at any desired location on the image surface. These subimages may be projected dependently or independently. The images may be moving or still.
In the case of multi-screen displays, there are the same number of (at least two) projectors as screens for projecting images onto the screens. As a result of their layout, the screens form a surface in the space which lies between the projectors and the viewer. There is a joint or seam where the screens which are positioned next to and/or above one another contact one another. With existing multi-screen displays, it is constantly being sought to limit the visibility of the seams between the assembled screens to a minimum for the viewer and to keep them at a minimum level over the course of time.
In practice, multi-screen displays are known in which a larger screen is assembled from a plurality of smaller screens or screen panels.
FIG. 1 shows a front view of a multi-screen display 1 according to the prior art, which is a combination of M screens 2 in the width direction and N screens 2 in the height direction, optionally with a stand 3 at the bottom. FIG. 2 shows a side view of the same multi-screen display 1, showing screens 2, supporting structures 5 (one per screen or one for a plurality of, or for all the screens together) and projectors 6. In FIGS. 1 and 2, some of the seams 4 between the separate screens 2 are indicated.
A multi-screen display may be composed of a number of identical basic units which are stacked on top of and/or next to one another as modules and are optionally attached to one another in addition. A basic unit of this nature is composed of a partially or completely light-screening, supporting structure, a screen which is mounted either fixedly or removably on the supporting structure or is mounted in front of or behind the arrangement of the multi-screen display, and a projector which is prefitted, optionally extendibly, entirely or partially in the supporting structure or is mounted in front of or behind the arrangement of the multi-screen display. Assembly by means of basic units requires a stable, perfectly flat supporting surface if, during installation, it is desired to obtain and retain an optimum connection between the basic units. Changing climatological conditions, such as temperature and relative atmospheric humidity, may alter the distance between the basic units and have an adverse effect on the connection between them.
FIGS. 3a, 3b, 3c and 3d together illustrate how, in the case of three combinations, one above the other, of a screen 7 and a supporting structure 5, differences in expansion cause the dimensions of the screens 7 to change with respect to the dimensions of the supporting structures 5 under the influence of climatological conditions. The screens 7 and the supporting structures 5 are illustrated separately from one another and are joined by means of auxiliary lines 8 in order to make the differences between their dimensions clear. FIG. 3a shows three correctly installed, adjacent screens 7 and supporting structures 5 under the nominal climatological conditions. In comparison to FIG. 3a, FIG. 3b and FIG. 3c show the screens 7 once they have become smaller with respect to the supporting structures 5 as a result of climatological conditions. In FIG. 3b, the three screens 7 are not attached any more to one another. Consequently, therefore, the seam 4 between two screens 7 becomes larger. In FIG. 3c, the three screens 7 are still attached to one another; the total screen surface area has become smaller while the seams 4 have in principle not changed. In FIG. 3d, by comparison with FIG. 3a the screens 7 have become larger with respect to the supporting structures 5 as a result of climatological conditions. The total screen surface area has become larger and the seams 4 have in principle not changed. Similar changes to those illustrated in FIG. 3 for screens which are situated above one another may also arise in the case of screens which are situated next to one another.
The effect of climatological conditions is important not only for multi-screen displays assembled from basic units but also for the multi-screen displays from the prior art which are described below and in which larger screens are obtained by joining together smaller screens, for example by adhesive bonding.
The basic units of the prior art which have been described above often have a frame around the screen, which frame holds this screen flat, often also serves to attach the screen to the housing of the basic unit and protects the edges of the screen from damage. This frame prevents an image from being projected all the way as far as the outer edge of the front side of the basic unit and makes the visual joint or seam between the basic units larger. EP-0 650 295 and EP-0 523 427 describe basic units of this nature and the assembly of a plurality of basic units of this nature to form a multi-screen display. A solution for allowing images to be projected right up to the edge of the front side of the basic unit is described in WO 95/28664 and consists in a special treatment of the outer edges of the screen and a special attachment of the said screen to a supporting structure, so that the light from the projector is able to reach the front edges of the screenxe2x80x94which are also the front edges of the basic unitxe2x80x94without being impeded. In principle, it is possible to achieve a perfect connection between screens of basic units at a specific temperature. However, the edges of a basic unit of this nature are fragile during transportation and the other drawbacks which are inherent to the assembly of basic units continue to exist.
Another solution is to adhesively bond together relatively small optical screens to form larger screens. Adhesively-bonded larger screens of this nature cannot be produced at the location where the projection screen is to be installed, but rather can be produced only at the premises of the constructor, following which they have to be transported in very robust and large packaging. In order to prevent damage and contamination to the screens during attachment to a supporting structure, installation has to take place with the greatest possible care.
U.S. Pat. Nos. 5,011,277 and 5,085,495 disclose projection screens comprising one or more horizontally arranged basic units comprising multiple screen panels which are arranged one above the other. The screen panels, a single front sheet, a single re-inforcing sheet and a support body are pulled together by means of wire and coil spring combinations. The horizontal seams between contacting screen panels arranged above each other are minimised. The vertical seams between screen panels of horizontally neighboring basic units are however not sufficiently minimised. Attaching basic units of this nature to one another not only has the abovementioned drawbacks which are inherent to the use of relatively large single screens or adhesively-bonded larger screens, but also drawbacks which are inherent to modular multi-screen displays assembled from identical basic units, such as the need for a flat and stable base and the fact that the connection between the basic units is dependent on temperature and humidity.
The abovementioned multi-screen displays which are known from the prior art are difficult to transport owing to their large dimensions and fragility and for installation often require lifting mechanisms, a large space around them and a number of qualified fitters. During installation, it is difficult or impossible to compensate for production tolerances in the dimensions of the components to be assembled and it is impossible to guarantee an optimum connection between the components to be assembled.
JP-08152677 describes a multi-screen display with a projection screen, consisting of a supporting frame body and a screen. The screen comprises several screen panels arrayed and arranged up and down and left and right, and horizontal and vertical light shielding plates. The screen panels and the light shielding plates have matching holes through which fit wires to stitch them together. The front edge of a light shielding plate is stitched to two mutually contacting screen panels on which it abuts, by means of wires, the two ends of which are fixed to the supporting frame body via, amongst others, two springs. The visibility of the so formed seams between mutually contacting screen panels is minimised. The screen hangs up at the top of the supporting frame body in a horizontal slider, and is pulled back to the supporting frame body by means of the springs which attach the stitching wires. At the bottom and on both sides, the screen can slide against the supporting frame body.
In order to obtain that the front edge of a light shielding plate remains close in touch which the mutually contacting screen panels with which it is stitched to form a seam, even in circumstances of expansion/shrinkage of screen panels caused by varying climatological circumstances, a light shielding plate should deform so that the seam can move. Such a movement of seams is however limited in at least two ways:
A light shielding plate is immovably fixed to the supporting frame body. Therefore, in the longitudinal direction said shielding plate cannot really move, it can only expand a little, which limits the movement of the corresponding seam attached to it. However, when the light shielding plate can bends, it is possible for the seam to move in a direction perpendicular to the longitudinal direction of the corresponding shielding plate.
At the short extremities of the light shielding plates, however, the perpendicular movement of the seam is limited by the light shielding plates which are attached at right angles with respect to the considered shielding plate, which light shielding plates cannot move in their longitudinal direction, as explained hereinabove. Therefore, at the short extremities of the light shielding plates, it is impossible for the seam to move in a direction perpendicular to the longitudinal direction of the corresponding shielding plate.
For above reasons, the light shielding plates can not deform enough to let the seams move in case of a non-negligible expansion/shrink of a screen. With a typical screen panel expansion/shrink of 0.7 mm per m per 10 degrees Celsius, screens of e.g. 10 m diagonal width can show seam movements of 10 mm. By consequence of this, in case of a non-negligible expansion/shrink of a screen, the screen panels and the corresponding seams have to move with reference to the edges of the light screening plates. If the stitches do not permit this, the screen panels will deform. If the stitching wires permit a move of the screen panels with regard to the edges of the attached light screening plates, e.g. because of looser tensioned stitching wires, minimised seams between contacting screen panels can not be guaranteed. For above-mentioned reasons, the solution of JP-08152677 is not sufficient to build larger projection screens.
Other disadvantages of the multi-screen display described in JP-08152677 are that not all the screen panels can have the same dimensions, and that the mounting of the wires is complicated and time consuming, both disadvantages complicating the mounting and replacement of screen panels.
The object of the present invention is to eliminate the abovementioned drawbacks.
The present invention relates to a projection screen for image reproduction devices, comprising a screen which is assembled from a plurality of, by preference identical, screen panels, a plurality of xe2x80x9clight screeningxe2x80x9d attachment plates and a supporting structure. The screen panels are provided at the edges with small holes in which joining wires are arranged, by means of which mutually contacting screen panels are drawn towards one another and by means of which screen panels are fixed to the attachment plates. The attachment plates thus present a part to which the screen panels are joined. Also the attachment plates and the supporting structure are joined together.
Of at least some of the attachment plates, at least the part to which screen panels are joined can make a guided longitudinal movement and can bend, or can hinge on to the supporting structure or another part of the same attachment plate which has an immovable join to the said supporting structure.
By a longitudinal move of an item is meant a move in the direction of the longest edge of the item. By a movable join between an attachment plate and the supporting structure is by preference meant a longitudinal move of the attachment plate with respect to the supporting structure and/or a hinging on to each other of the said attachment plate and the supporting structure. By hinging of a first item on to a second item is meant that the first item and the second item form a hinge, whether or not physical axes of a hinge are present.
The attachment plates are preferably horizontal and vertical attachment plates, which are provided with small holes for fixing the joining wire. A combination of deformable and non-deformable attachment plates may be used. By deforming of an attachment plate is by preference meant bending and/or a longitudinal move of two parts of the attachment plate with respect to one another and/or a hinging of two parts of the attachment plate to one another.
The screen panels are preferably optical panels, such as a Fresnel lens, a lenticular or a combination of the two and have a perfectly rectilinear edge. They may comprise a plurality of layers, of which at least one layer is attached to the attachment plates with the aid of joining wires.
In order to draw the screen panels towards one another and to position them with respect to one another, and in order to fix these screen panels to and position them with respect to the attachment plates, use is preferably made of rigid joining wires which are U-shaped and are made from metal or plastic.
The seams between the screen panels which have been drawn towards one another are minimal, with a size of less than half a millimeter. Drawing the panels together by means of joining wires ensures that the seams between the screens are always, and remain, minimal, in spite of manufacturing tolerances and under changing climatological conditions, such as temperature and relative atmospheric humidity. Any differences in expansion/shrink between the screen panels, on the one hand, and the supporting structure of the projection screen, on the other hand, are absorbed by the fact that the attachment plates which join together the screen and the supporting structure are deformable and/or have a movable join to the supporting structure (13), and the fact that the joining wires can be deformed to a limited extent in order to keep the join between the screen panels optimal. As a result, the screen can move with respect to the supporting structure, within certain limits, in such a way that the seams remain minimal.
The attachment plates have a number of functions, such as, inter alia, attaching and positioning screen panels, bearing the weight of one or more screen panels, deforming in order to allow movement of the screen, and providing separation between light emanating from projectors which are positioned directly next to or above one another.
The horizontal attachment plates are preferably assembled from a plurality of plates which are attached to one another and one of which is attached to the supporting structure and to one of which the screen panels are attached. The horizontal attachment plate preferably has a greater rigidity in the downwards direction than in the upwards direction, in order to be able to bear the weight of one or more screen panels.
The vertical attachment plates preferably consist of a single plate which can be attached to the supporting structure and to which screen panels can be fixed, or is composed of a plurality of plates which are joined to one another and one of which is attached to the supporting structure and to one of which the screen panels are fixed. In order to be able to absorb the movement of the screen and/or the screen panels, the vertical attachment plate preferably bends or hinges to the left or to the right and is able to slide up and down, together with the screen panels connected thereto, with respect to the supporting structure. An attachment plate to which the screen panels are fixed is preferably made from a non-transparent, matt and black plastic which has approximately the same coefficient of expansion as that of the material used for the screen panels and is preferably provided with small holes for fixing the joining wires of the screen panels using nuts and bolts.